O'Sullivan, who has won the UK title four times, twice fell behind before the interval against Duffy and looked short of his best.

His erratic performance was summed up in the sixth frame which ended when, needing a snooker and attempting to clear the pink from the jaws of a pocket, he smashed it off the table and also went in-off for the fourth time in the frame.

O'Sullivan, who chose to sit out most of last season, plans to "play the system" before taking another break.

Who would have thought that - an amateur, through to the last 32, beating two top-class players?

Mitchell Travis

He said: "My goal is to get enough prize money so I can take another break from snooker. I can have a holiday, sit at home and chill again, which is great."

O'Sullivan will face Scotland's Marcus Campbell in the next round while Trump, who wrapped up his victory with a 133 break, will meet either Michael Holt or Mark Allen.

Defending UK champion Selby was forced to fight back from 3-1 down to set up his third-round clash with Grimsby's Stuart Carrington.

Selby told BBC Sport: "In patches I played OK, but there were a lot of balls that I missed that I probably should have got.

"It shows that my battling quality is still there. I'd have rather won the matches a lot more convincingly but at the end of the day I'm still in the tournament, and that's the main thing."

Robertson was dominant against Williams, completing his 52nd century break of the season in the sixth frame with a double on the black for 119, and wrapping up victory soon after.

The Australian told BBC Sport: "Robbie is really inexperienced on TV so I went for a lot of shots today, let him beat himself up really - I know what that's like on TV. I kind of bullied him a bit."